Thermoplastic polyurethanes (TPU's) are well known. These materials are elastomers which are useful in a variety of applications e.g., in wire and cable jacketing, calendared film, adhesives, automotive parts such as bumpers, roller skate and skateboard wheels, and as the binder in magnetic recording media. Thermoplastic polyurethanes are linear polymers which can be processed in conventional rubber and/or plastics processing equipment. TPU's can be milled, injection molded and calendared, for example. Physical properties, such as hardness and modulus vary depending on chemical compositon.
Thermoplastic polyurethanes are prepared by reacting one or more glycols with an organic diisocyanate (or, less commonly, a mixture of organic diisocyanates). Typically a mixture or blend of glycols, e.g. a macroglycol and one or more low molecular weight aliphatic glycols, is used. The macroglycol may be a hydroxyl terminated polyester, polyether or polycaprolactone polymer or oligomer, which typically has a molecular weight from about 500 to no more than about 10,000. The low molecular weight aliphatic glycols generally contain from 2 to about 12 carbon atoms. Representative low molecular weight aliphatic glycols include ethylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol and diethylene glycol. The low molecular weight glycol or mixture thereof is commonly called a chain extender. A thermoplastic polyurethane prepared from such macroglycol, one or more low molecular weight glycols and organic diisocyanate is generally characterized by the presence of both hard and soft segments.
An early patent on linear thermoplastic polyurethanes and their preparation is U.S. Pat. No. 2,871,218 to Schollenberger (issued in 1959). A number of patents have been granted and various technical journal articles published on thermoplastic polyurethanes since then. Among the patents are U.S. Pat. Nos. 4,284,750 (Amirsakis) and 4,643,949 (Kolycheck et al), both direct to TPU for magnetic tape.
U.S. Pat. No. 4,695,604 to Amirsakis discloses electron beam curable polyurethanes which are reaction products of a hydroxyl terminated polyester, a compound having ethylenic unsaturation, and at least 2 hydroxyl moieties, optionally a chain extender which is a lower aliphatic or cycloaliphatic diol, and a stoichiometric amount of a diisocyanate. The unsaturated compound may be an allyl dihydroxyalkyl ether (e.g., glyceryl allyl ether) or a dihydroxyalkyl methacrylate (e.g. 2,3-dihydroxyalkyl methacrylate). The electron beam curable polyurethane typically has short chain unsaturated aliphatic pendent groups.
Other photopolymers having photocrosslinkable maleimide pendent groups are known. For example, Roth et al, "DMI-Photopolymers and Their Technical Application," paper given at Radcure, Europe, 1987, pages 5-11 to 5-23, describes acrylic polymers having photocrosslinkable dimethylmaleimide groups. Aromatic polyamides with maleimide pendent groups which are either heat or photocrosslinkable are disclosed in de Abajo et al., Die Angewandte Makromolekulare Chemie, vol. 111, 1983, pages 17-27 (no. 1698). Other imide pendent groups are also discussed.
U.S. Pat. No. 4,107,174 to Baumann et al., also discloses certain photocrosslinkable polymers having imidyl pendent groups. U.S. Pat. No. 4,642,353 to Berger shows various photocrosslinkable polymers, among them certain polyurethanes (formulas XV and XVI of Berger) containing imidyl groups linked to the polymer chain through a sulfur atom and an alkylene, arylene or substituted arylene group. (In contrast, polymers of the present invention contain no sulfur). These photocrosslinkable polymers are prepared by reaction of an unsaturated polymer with an imidyl compound having an --SCl or --SH end group. Preparation of the polymers described in this patent would present environmental problems, i.e. both odor and toxicity, because, of combined sulfur present in both the non-polymeric reactant and the polymer product.